The invention relates generally to an electrohydraulic valve assembly and, more particularly, to an independent metering valve having a fluid make-up function.
An independent metering valve includes a first pair of independently controlled electrohydraulic displacement controlled spool valves for controlling pump-to-cylinder communication between an inlet conduit and a pair of control conduits and a second pair of independently controlled electrohydraulic displacement controlled spool valves for controlling cylinder-to-tank fluid flow between the pair of control conduits and an outlet. Each of the spool valves has a displacement controlled solenoid valve for controlling the position of the spool valve. The spool valves are normally biased to a closed position and are selectively actuated to provide several modes of actuation.
This system can provide many functions normally requiring separate valves simply by actuating one or more of the four independently controlled electrohydraulic displacement controlled spool valves. However, one problem that arises is that the pressure control functions requiring fast response, such as pressure relieving and fluid make-up, typically require a line relief valve and a fluid make-up valve, respectively, to be installed on an actuator supply conduit. Both the line relief valve and fluid make-up valve are, many times, large in size and capacity.
In a more recent development, as disclosed in U.S. Pat. No. 5,868,059, the valve element of an independent metering valve includes both the fluid relief function and the fluid make-up function. A fluid make-up means provides communication between the control chamber of the valve and an actuator supply conduit so that the valve element moves to an open position when the fluid pressure in the supply conduit drops below a predetermined level. However, this independent metering valve has a relatively complicated valve structure.
The present invention is directed to overcoming one or more of the problems set forth above.
In one aspect of the present invention, a control valve in fluid communication with an actuator to controllably move an output member of the actuator may include a valve body defining a passageway, a pressurized pilot supply fluidly connected to the passageway, and a fluid reservoir fluidly connected to the passageway. A pilot operator is selectively moveable within the passageway, and a flow metering operator is moveably disposed within the passageway. A fluid make-up operator is disposed in the passageway and in fluid communication with the fluid reservoir and the actuator. The fluid make-up operator operates to direct an amount of pressurized pilot supply fluid in response to a decrease in actuator pressure coinciding with a cavitation condition within the actuator. A control chamber within the valve body is structured and arranged to contain pressurized fluid from the pressurized pilot supply. The control chamber is in fluid communication with the flow metering operator. The flow metering operator is urged to fluidly connect the actuator with the fluid reservoir under the influence of the pressurized fluid within the control chamber through activation by either the pilot operator or the fluid make-up operator.
In another aspect of the invention, a method for controllably moving an output member of an actuator includes supplying a pressurized pilot supply fluid to a passageway defined by a valve body. The passageway includes a control chamber. The method also includes selectively moving a pilot operator within the passageway and controllably moving a flow metering operator within the passageway to provide fluid communication between the actuator and a fluid reservoir. A fluid make-up operator is provided in the passageway and in fluid communication with the fluid reservoir and the actuator. The method includes operating the fluid make-up operator to direct an amount of pressurized pilot supply fluid in response to a decrease in actuator pressure coinciding with a cavitation condition within the actuator, and activating either the pilot operator or the fluid make-up operator to urge the flow metering operator to fluidly connect the actuator with the fluid reservoir under the influence of the pressurized fluid within the control chamber
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.